1. Field of the Invention
The present invention relates to a propylene polymer composition which has not only an excellent adhesion to polyurethane without the use of a primer, but also has a good weathering resistance. More specifically, the present invention relates to a propylene polymer composition which comprises (A) a modified propylene polymer obtained by treating (1) a propylene polymer or a mixture of a propylene homopolymer and a ethylene-propylene copolymer rubber with (2) an organic compound having at least one unsaturated bond in the molecule and a hydroxyl group and (3) an organic peroxide and (B) a propylene polymer, and may further comprises one or more of (C) an amorphous ethylene-propylene copolymer having a propylene content of 20% to 50% by weight and a Mooney viscosity at ML.sub.1+4 at 100.degree. C. of 20 to 100, (D) a high-density ethylene polymer having a density of 0.935 g/cm.sup.2 or more, (E) a linear low-density ethylene copolymer having a density of not less than 0.900 g/cm.sup.3 but less than 0.935 g/cm.sup.2, a melting point of 106.degree. C. to 130.degree. C., a melt flow rate of 0.01 to 100 g/10 min and substantially having 3 to 35, based on 1000 carbon atoms of the backbone carbon chain, of the side-chain alkyl groups having 1 to 10 carbon atoms, and (F) an inorganic filler. The resultant propylene polymer composition not only has excellent mechanical characteristics such as rigidity and impact resistance, but also has an excellent adhesion to polyurethane without the use of a primer. Furthermore, when the high-density ethylene polymer and/or the linear low-density ethylene copolymer are incorporated into the composition, an excellent usual appearance, especially an excellent glossiness can be obtained.
2. Description of the Related Art
As is well known, propylene polymers (propylene homopolymers, propylene copolymers) not only have an excellent moldability but also have good mechanical characteristics, heat resistance, solvent resistance, oil resistance, and chemical resistance, and therefore, are produced widely in industry and utilized in various fields such as industrial parts for automobiles, electrical instruments, and electrical machines, as well as commodities. However, since the molecules thereof have no polar group (so called non-polar type), they have a poor adhesion to polyurethanes and thus various problems arise. These problems are described herein by referring to bumpers for automobiles, as widely utilized, by way of example.
Heretofore, bumpers made of metals or polyurethanes have been widely used. In recent years, due to the demands for weight reductions and cost-reductions of automobiles, bumpers made of propylene polymers (propylene homopolymers, ethylene-propylene random or block copolymers) or a composition mainly comprising propylene polymers have been widely utilized. These bumpers are frequently used after a previous embossing as originally attached without the application of a coating. However, to impart a further brilliance and a sense of high quality, in many cases the bumpers are mounted on cars after the application of a coating of a polyurethane coating material which is in line with the increasing demand for higher quality automobiles.
However, the molecules of propylene polymers have no polar group, as mentioned above, and thus are chemically very inactive polymeric substances. Therefore, when coating a polyurethane, it is well known in the art to apply a pretreatment to the molded product, such as an electrical treatment (e.g., corona discharge treatment, plasma treatment), mechanical surface roughening, flame treatment, and oxygen or ozone treatment. Further, prior to these surface treatments, it is recommended to wash the surface with a solvent such as an alcohol or aromatic hydrocarbon. Further, it is known to dip the molded product in an organic solvent such as 1.1.1-trichloroethane, perchloroethylene, pentachloroethylene, etc., at a temperature near boiling point or expose it to a solvent vapor (for example, "Course of Plastic Materials Vol. 7, Polypropylene Resin", p. 218 to 219, ed. by Kaneyuki Takagi & Heizo Sasaki, 1969, published by Nikkan Kogyo Shimbun K. K.). However, according to these methods, not only is a special treatment equipment required, but also a considerable time is required for such treatment.
Further, according to current practice, the molded product (bumper) is applied with a sub-coating of a primer which will adhere to the propylene polymer and a polyurethane coating material is applied as the top coating. That is, the following steps are required; primer sub-coating.fwdarw.baking.fwdarw.polyurethane coating.fwdarw.baking (2 coats-2 bakings or 3 coats-2 bakings), and the coating steps require a long time (usually about 1 hour and 30 minutes). For this reason, the coating cycle is prolonged the production of bumpers coated with polyurethane, whereby not only is bulk production rendered difficult but also the cost is increased.
In the production of other automobile parts, tricycle parts, electrical instrument parts, and electronic instrument parts, similar problems are involved when propylene polymers are employed and coated with polyurethane, although the coating method may be different.
In general, polypropylene polymers or compositions thereof utilized for bumpers, etc., incorporate UV-absorbers, UV-stabilizers, and antioxidants, etc., according to a combination of any desired recipe, for a reinforcement of the weathering resistance. After several years of actual use, however, the surface of the molded product will be discolored or chalking or cracks may form thereon. Thus, a satisfactory result cannot be obtained under the present situation. Further, there is an increasing demand for a better grade of bumper, particularly as the taste for higher quality cars is augmented and the frequency of use in bad weather areas increases.
Accordingly, to cope with such a trend, it may be considered to increase the amount of weather-resistant formulation or add new additives. However, a mere increase in the amount or addition of these may cause problems in appearance in molding (e.g., lustre irregularity or whitening of the surface), or the increased amount of or newly added additives may bleed out on the surface of the molding to worsen the appearance or result in whitening of the surface of the molded product after prolonged actual usage.